shrimp, plecos and cories are good bottom feeders. shrimp and cories eat excess food that falls in the gravel. shrimp also will eat algae. most plecos eat algae but can produce lots of waste.
I DO NOT recommend crayfish at all in with any kind of fish. unless you're planning to feed the crayfish to the fish or vice versa.
If you cut off his claws, the fish will eat him. he's defenseless and the fish sees an easy meal.
If you leave his claws, he will tear up the fishes fins and when the lights are off, the fish becomes a midnight snack for the crayfish.
I had a Florida blue crayfish. I made the mistake of putting him in with my other fish. They were danios and white clouds, pretty fast moving fish. but after i witnessed the crayfish snatch a danio that swam quickly by him and proceed to eat him, i moved the crayfish to a tank by himself with just a few feeder platy and guppy fry.
also when crayfish molt, they are exposed to everything and the tiniest little thing can kill them. my crayfish died after he molted.